1. Field of the Invention
The present invention relates to a family of integrated filter forward converter having continuous input and output currents.
2. Description of the Prior Art
U.S. Pat. No. 5,523,936 issued to Leu et. al. discloses a built-in input filter forward converter for dc-dc applications and U.S. Pat. No. 5,640,318 issued to Leu discloses another forward converter for off-line applications. FIGS. 1A and 1B illustrate such two prior arts of forward converter each having input filter function being magnetically included in the transformer assembly. Wherein power switch, clamp diode and two cross-coupled capacitors are respectively connected to a split-winding transformer. When the power switch is turned off, the transformer leakage inductance and cross-coupled capacitors form an effective input filter without interrupting the input current of the converter. Hence, continuous input current is maintained with no external input inductor required. However, both patented forward converters are single-ended, that is, both only operate as half-wave mode and still require an output filter inductor for smoothing the output current. A full-bridge topology that integrates transformer and output inductor magnetic functions into common magnetic assembly in U.S. Pat. No. 5,555,494 to George Q. Morris. FIG. 1C illustrates such a prior art of forward converter. However, Morris converter requires a large input filter to reduce the noises caused by a pulsating input current of a full-bridge converter.